Tuning thermionic amplifier



March 26, 1929. w, M,.BAILEY 1,706,838

TUNING THERMIONIG AMPLIFIER Filed July 14, 1923 INVENTOR I Willzkzm MBazZe Patented Mar. 26, 1928.

UITEDHSTATES. PATENT oFFicE.

WILLIAM 1W, BAILEY, OF LYNN, MASSACHUSETTS, ASSIGNOR TO WIRELESS SPECIALTY APPARATUS COMEANY, 01* BOSTQN, MASSACHUSETTS, A COBIORATION OF NEW YORK.

TUNING TI'IERMIONIG AMPLIFIER.

Application filed July 14,

This invention relates to radio apparatus and method, and particularly to the same for the purpose of selecting desired natural periods of the circuits of transformers employed to couple thermionic tubes or audions forming parts of a radio amplifying receiv ing set.

The object of the invention is to provide apparatus which will permit convenient execution of the novel method by the user, such apparatus to be of low cost and of practical, sturdy construction.

The invention consists of the apparatus and method shown and described in the aC- companying drawings and following description.

Of the drawings, Figure 1 is a diagrammatic illustration of a noval form of apparatus suitable for eiiecuting the novel method; and Fig. 2 a view of a unit panel construction embodying the essence of the invention and suitable for use as a portion of a radio amplifying receiving set, this portion comprising novel forms of transformers cooperating with suitable switching means.

'A modification of the invention is shown in Figs. 3 and 4, whereof Fig. 3 is a diagram similar to Fig. 1, and Fig. 4c a detailed view of the modified form of controlling means shown in the diagram Fig. 3.

t now the practice, in thermionic tube amplifier receiving sets, to couple successive tubes by a transformer, such transformer and its circuits being designed to have a natural period adapted to give best results when the period of received communications is substantially the same an that of the circuits. In such apparatus, when the received coinnninications have a substantially different period or frequency from that of the transformer circuits, the eliiciency of the set is much less. Itwould be possible, although not practicable, to take oil tap leads from portions of the secondary or primary wind ing of the transformer, to suitable switches, so that the period of the transformer circuits could be varied and thereby adapted to the period of the received communications, so as to maintain a constant efficiency of the system for all received frequencies. That is not desirable as a practical matter, however, on account of the difficulty of making and maintaining proper connections between such tap 1923. Serial No. 651,486.

leads and the secondary or primary winding of the transforn'ier. In particular, the wine compris ng the transformer secondary is usually so fine as to make it very ditlicult, if not impossible, to maintain the connections of the tap leads thereto in service, even after the diflicult feat had been accomplished of making such connections in the first instance. Also, on account of the high frequency currents existing in the set, the capacity effects resulting therefrom in the tap leads would very seriously conflict and injuriously affect the operation of the entire apparatiiis.

In this invention, there may be employed coupling transformers of the ordinary type employed in thermionic amplifier sets, as above, where the two circuits have substantially the same natural period, a line wire secondary of relatively large number of turns being wound on a laminated iron core, and a primary being wound over the secondary or the primary could be wound first on the core and the secondary over it; or the primaryand secondary could be wound side by side; and while now it is preferred to employ such iron core, it could be omitted.

In effect, this invention comprises a means for varying the effective tuning of the two like-tuned circuits of the transformer to various wave lengths (periods or frequencies) without the necessity of tuning by variation of actual inductance or capacity in either circuit of the transformer, and particularly without varying the amounts in circuit of the primary or secondary winding of the coupling transformer.

In accordance with the invention, the transformer or transformers in the set are designed, as to their primary and secondary windings, preferably to receive at maximum efiiciency the highest wave length of the various receivable wave lengths of several different frequencies. For example, in the present practice of radio telephonic broadcasting, 550 meters is the highest wavelength, and transformers of this invention. may he designed, as to their primaries and secondaries, to receive at maximum elliciency at such wave length. The remainder of the apparatus hereof has for its purpose to reduce the effective natural period of the transformercir'cuits to various lower degrees of wave length, so that the set, without any action by the operator directly on the primary or secondary of the transformer or on any tuning'inductance or tuning condenser, can be adapted to receive at maximum efficiency any transmitted communication of such lower wave lengths.

Fig. 1 shows an ordinary present-day form of audion amplifier set,as well known,

which is provided with the additional ap paratus of this mventlon and comprising, for

-each transformer, a third or tertiary coil associated with the transformer. isa transformer A, coupling a pair of audlon T which is preferably stationary and closely In Fig. 1

tubesU U which, as shown, are amplify- 1 ing tubes acting on received radio frequency currents. Transformer A is designed,- pur- 'suant to well-known practice, to operate with a pivoted switch S which, as indicated by the arrowhead, can make contact with successive portions of winding T so that greater or less portions of winding T are included in circuit with the switch S and thereby are short-circuited or shorted. Tertiary T is closely associated with transformer A, as by winding ontop of the transformer windings- P, S, for example;

and owing to such close association, wind ing-T acts, when shorted (and shorted portions of it act to reduce the effective inductance of the transformer, and hence reduce the effective periocbor tune of the transformer. (and its circuits), i. e., to reduce the wave length at whichthe transformer acts at maximum efficiency-when connected in any such' receiving set or amplifier train as that shown in Fig. 1.. The tertiary winding T may be arrui'iged in various relations with the-windings of the transformer, provided only that it be in substantially close inductive relation therewith.

In the apparatus of Fig. 1, a third audio tube D is employed as a detector (having grid leak GL and gridcondenser GC), and

this third tube is coupled with the previoush acting amplifier tube U -by a transformer B which may be a duplicate of transformer A, and having a similar primary]? and secondary S. This transformer B also may be, and preferably is,'provided with a tertiary winding T like tertiary winding T associated with transformer A; and winding T may beprovided with pivoted switch S like S for winding Tf for the purpose of shorting portions of winding T Also the upper ends of the two tertiaries, T and T may be connected by lead L, as shown, in cases where switches S and S are to be combined to operate as a unit or under one control as shown in Fig. 2. As indicated also, each of transformers A and B may he providedwith a laminated iron core C.

In Fig. 2 is shown a panel or base of bakelite or other insulating material. I) on which are mounted transformers A and B of Fig. 1, with iron cores 0. In the case of each transformer, a n'imary P is wound directly on core C, a secondary S is wound over such primary, and a tertiary coil ('l and T for the two transformers) is wound over the fine wire secondary S. In the use of the invention thus far, four turns of each tertiary coil are wound .on the outside of the transformer windings. The wire for the tertiary coil is a coarse insulated wire, about No. 20 B. & S. gauge stranded or solid wire. The coils of primaries I and secondaries S may be of any design, as well known, save that they are such as to provide a natural period for the circuit corresponding with the highest wave length expected 10 be received. To each turn of the tertiary winding, at a bared portion thereof, is soldered a lead. In the case of the left-hand transformer, four of such leads extend to switch points 1l-, and from one end of the tertiary coil a lead L is taken which extends to a corresponding lead L extending to the end of the right-hand tertiary coil T, both of which are connected by lead L to the short-circuiting switch S 2. The tour re maining leads from the right-hand tertiary coil T extend to right-hand contacts 1--1larranged in reverse order to contacts 14 of the left-haml tertiary T Switch 3, 2 is provided with two extensions 5, 6 which play over the respective series of contacts at left and right. Each series of contacts also includes a switch contact point 0. W hen switch S 2 engages contacts 0, (l. no portion of either tertiary is shorted and the influence of the tcrtiarics is nil, so that transformers A and I) operate at their normal or natural period, i. e., prcfcrablv that of the longest wave length receivable. \v'hcn the switch engages the two contacts 1, I, one turn of each of the two tcrtiarics (1, T is shorted, so that the cll'cclivc induc tance of the windings of both transformers is reduced, and. hence the cil'ective periods of the transformers is reduced so that they may operate at maximum clliciency at some received wave length between say 5.30 meters (the highest receivable) and say 250 meters, the lowest wave length employed in present radio telephonic broadcasting. lVhcn the switch is on contacts 2, 2, and respectively on contacts 3, 3, two and three turns respectively of the two tertiaries are shorted so that the transformers act ellicicntly on yet lower intermediate frequencies between 550 meters and 250 meters. And when switch S 2 engages contacts i, a, all of each tertiary is shorted to permit the trans formers to act eliiciently at 250 meters.

The unit of Fig. 2 to be employed as a portion of a complete receiving set, base E serving as a panel, box side or .subpanel, and the terminals of the primaries and secondaries of the transformers being connected in the circuits of the set as indicated in F 1, and for that purpose extending to the circuits of the other apparatus inside the c sing or box for the entire set. Fig. 2 shows the inside of the panel and the switch located on the inside of the panel; and pursuant to common practice, a control knob (not shown) on the outside of the panel is connected to the switch mounted on the inside wall of the panel.

Each unit of Fig. 2 may comprise either two transformers as shown, or a single transformer, or more than twotransformers, corresponding with the number of tubes used in the set, a common switch for all being provided by preference. In Fig. 1 the input is indicated at I at the left, and from the right of the diagram the usual connections are to be made to the usual batteries and indicating apparatus, such as telephones or loud speakers. The tubes U U and D are shown by their usual conventions of grid, plate and filament, and such tube elements are to be connected in the circuits with the batteries in the Well-known manner.

The control afforded by the execution of this method is a very perfect one, and, as indicated in Fig. 2, may be elfectuated by a single controlling handle, so that the wave length of the entire set may be altered by a single control. Also the construction as to the tertiary coils is very simple, practicaland inexpensive.

In the modification shown in Figs. 3 and l, a resistance It is acted on by the switching means as an alternative to the cutting in and out of portions of the tertiary by the switch. This permits a complete elimination of tap leads of Figs. 1-2 from intermediate points of the tertiaries or auxiliary inductances to the control switch, the only leads from the auxiliary inductanccs in this modification being from their ends to the control switch via the rheostat. In the diagram of Fig. 3, the tortiaries '1, T respectively are provided with resistances it and it, and the switch S 2 is disposed relative to said two resistances so as to act to cut them gradually in or out sinuiltaneously. Switch S 2 in this case is really the operating member of a rheostatu This modification is shown in detail in Fig. 4, wherein the two resistances R and R and switch S 2 are mounted on an insulating base E; thus illustrating that in any case the switch and its contacts or resistances may be mounted on a base independently of the transformers as distinguished from the form shown in Fig. 2. In Fig. 8 is shown also at X the combination in the set of a variable stabilizing resistance X in accordance with my application, Serial Number 644,832, filed 12 June 1923.

As an alternative to the use of the unit panel shown in Fig. 2, the transformers may be disposed in the set in any ordinary fashion, and switch S 2 be located at any convenient point of the panel of the set for easy control by the user; and in such cases the leads from the tertiaries to the switch may be bunched together and led through an insulating tube (not shown) secured to the interior of the casing of the set. In such case (asdistinguished from the case of tap leads from the secondary or primary of the transformer), there is no resulting harmful action of capacity effects involved in the leads, for the reason that in the case of this invention the tertiary winding comprises only a few' turns (as four shown), so that therefore the voltage from turn to turn of the tertiary is quite low, on account of the large ratio between such tertiary and the transformer primary comprising, for example, 150 turns more or less. The voltage be tween turns of the tertiary being low, therefore the voltage from tap lead to tap lead is low, thereby resulting in lack of deleterious capacity effect in the leads.

In the modified form of the invention shown in Figs. 3 and 4, the ultimate operation is exactly the same as in the forn'i of Figs. 1 and 2, in the sense that the control pern'iits limitation of the current in the tertiary which is effective upon the transformer, i. e., in both cases the control is of the ampere turns of the current inducedin the winding of the tertiary by the transformer. In Figs. 3 and l, however, the operation in detail is specifically different, in that the resistance limits or varies the current flowing in the permanently completely shorted tertiary (through the resistance), so as to control the effect of the shorting winding on the effective inductance of "thetransformer. In both cases, the tertiary is variably shorted; in the case of Figs. 1 and 2 by successively shorting different portions of the tertiary coil; and in the case of Figs. 3 and i by the permanent shorting of the entire tertiary coil but via the variable resistance by which the degree of effective shorting is continuously changed. In both cases, the ultimate result is control and variation of the effective wave length of the transformer.

In Figs. 3 and 4, the lower the resistance R in circuit with the tertiary, the shorter will be the effective wave length of the transformer; because then more current is allowed to flow in the tertiary, thereby re-- Ill) dt'lcing the effective inductance of the transformer and therefore reducing its effective An advantage of wave length. V the modification of Figs. 3 and 4 is not only the elimination .of tap leads from transformer primary P'or secondary S, butalso the elimination of all intermediate tap leads from the tertiary fwindingp Another advantage of the modification ofl i'gs 3 anda is thatas distin guished from the step-by-step operation of Figsrl and 2, the resistance control affords a smooth and even change of wave length, which adapts the set to maximum efficiency for absolutely all wave lengths between the maximum and minimum receivable wave lengths.- If the leads be short between the Qte'rtiary and the rheostat, the value of the resistance.

resistance itself may be made very low, the total permissible value for each resistance being as low as six ohms.

In Figs. 3 l,Rinay.be taken to illustrate an inductance coil variable b switch S 2 or a'variablecapacit in lieu of an ohmic condenser in the circuito'f the shorting coil T or T? permits a comparatively rough tuning of the transfer-incrz I have found that either an inductance coil or an ohmic resistance is preferable to a condenser capacity, because they are cheaper and operate more uniformly. The addition of inductance or resistance to the circuit of the duced slightly increasing wave lengths.

Butthe resistance, tuning coil and condenser me included broadly as equivalents herein asreactances generally.

If desired, in any case, the shorting winding of any embodiment of the invention niay be connected to ground- VVhle it is preferable to employ a doublewinding or inductive type of transformer as shown, yet it is pcrimssible within the invention to employ a single coil-or autotransfer-men I clai1n v 1. The means, as a unit portion of a thermionic amplifying apparatus, for simulta- 'neeuslyvaryingthe effective wavelength of the circuits of a succession of transformers he employment of a variable mosses which couple succcssim audion tubes, which tube-transformer circuits have a natural period at which a given received wave-length is efiiciently received, said means comprising a panel of insulating material having mounted thereon at least two of such coupling transformers; a corresponding number of auxiliary iiuluctances arranged respectively in inductive relation with the two windings of the successive transformers but not electrically connected to either of them, whereby the clt'cclive short-circuiting of said auxiliary inductanccs reduces the effective inductances of the windings in the successive transformers; switching moans also mounted on said panel: and leads between said auxiliary inductances and said switching means whereby the operation of the latter simultaneously varies the naturalivavc-lcngth circuits as to their cllcclivo wave-length without variation of their natural wave-length.

2 The means for rei'luciug the effective wave-length of both circuits of a trans former which couples a pair of audion tubes, which tube-transformer circuits have a natural wave-length receiving elliciently a high wavelength, said means comprising an inductance in close inductive relation with each of said transformer windings in the two tube circuits; and means for shortcircuiting more or less of said inductance, thereby reducing the ell ective inductance of the transformer windings and reducing the effective wave-length of said high wuvelength tube-transformer circuits, permitting the apparatus to receive cllicicnl'ly a wavelength lower than the natural wave-length of the circuit.

'lhe nieans for simultaneously varying), the ell ectivc wave-length of the. circuits of a succession of transformers which successively couple successive audion tubes, which tube transformcr circuits have a natural period at which a given rcccivcd \vavwlcngth is efliciently received, said means comprising a number of amiiliary inductunccs correspond-ing in number with such transformers and respectively in inductive relation with the portions of the successive transformers which are connected in the respective tubecircuits; :1 common switch; and leads bctwcen said m -h and the lcspccllvc auxiliary inductzmccs, whcrcby the operation of the switch simultaneously varies the effecthe inductance of the portions of the suc cessive transformers in :erid circuiis and therefore varies the effective wave-length of the said circuits.

lVILLIAM M. BAILEY loo llli') Ill) 

